Mice that are heterozygous for the targeted allele are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. Homozygous null mice have an embryonic lethal phenotype, failing to develop past 9.5 days post coitum. Homozygous mutant mice exhibit ventral cyclopia and holoprosencephaly. During development homozygous mice fail to undergo embryonic turning, closure of the ventral midgut and normal rightward looping of the heart. The embryonic heart remains a linear tube. This mutant mouse strain represents a model that may be useful in studies of tumors and neural tube defects due to disruption of the hedgehog pathways. When bred to a strain with loxP sites inserted into the same targeted allele (Stock No. 004526) and a strain expressing Cre recombinase in the skin (Stock No. 004782), this mutant mouse strain may be useful in studies of hedgehog signalling and cell proliferation in the dental epithelium. When bred to a strain with loxP sites inserted into the same targeted allele (Stock No. 004526) and a strain expressing Cre recombinase in the nervous system (Stock No. 003771), this mutant mouse strain may be useful in studies of hedgehog signalling and cerebellar foliation. When bred to a strain with loxP sites inserted into the same targeted allele (Stock No. 004526) and a strain expressing Cre recombinase in the midbrain/dorsal spinal cord (Stock No. 007807), this mutant mouse strain may be useful in studies of craniofacial development. The Jackson Laboratory 2024, used with permission.